Problem: William eats at a cafe and the cost of his meal is $\$28.00$. He would like to leave a $20\%$ tip. What is his total bill including tip?
Answer: The tip amount is equal to $20\% \times \$28.00$ We can find the tip by first calculating a $10\%$ tip and then multiplying that number by two. To calculate a $10\%$ tip, move the decimal point in $\$28.00$ one place to the left. $10\%$ $\times \$28.00$ $\$2.80$ To calculate a $20\%$ tip, multiply the $10\%$ tip amount by two. $20\%$ $\times \$28.00$ $\$2.80$ $ \times 2 = $ $\$5.60$ The cost of the meal plus the amount of the tip will equal the total bill amount. $\$28.00 + \$5.60 = $ $\$33.60$ The total cost of the bill is $\$33.60$.